The lifetime of such a cell is known to be limited by the low cycling yield of lithium and by the appearance of dendrites during recharging. In practice, it is necessary to use three to five times as much lithium as the quantity theoretically required. The main cause of failure in this type of cell comes from the dendrites which can give rise to internal short circuits. These short circuits give rise to localized heating which, in the presence of the finely-divided alkali metal and of the organic electrolyte can give rise to a battery explosion.
Proposals have already been made to use an optimized electrolyte composition (solvent, solute, additives) to improve the cyclability of the cell and to limit the effects of dendrite growth.
It is also known to replace pure lithium with alloys (such as LiAl, LiB, LiSi, . . .) for improving the reversibility of the negative electrode.
However, the above dispositions provide results that remain inadequate.
According to articles published in:
Powers 1990 Lithium Battery Report; and
Journal of Power Sources, 34 (1991), 31-38; it has been shown that increasing the pressure exerted on the anode makes it possible to obtain a significant increase in the lifetime of the cell. This pressure is provided by mechanical means on assembly. Thus, for a cylindrical cell having wound electrodes, the spiral winding is tight.
An object of the present invention is to provide compression means that are easier to implement than the previous mechanical means, and that are capable of accepting larger changes in size during operation of the cell.